The invention is directed to a brush retainer for a DC motor, and more particularly to a brush retainer that prevents contact between the brushes and a commutator during motor assembly.
FIG. 1 is an exploded view of a portion of a known motor assembly 100 in which the inventive device will be used. Of particular interest with respect to this application is the interaction between a brush holder 102, brushes (not shown) that are held in the brush holder 102, armature shaft 106, and commutator 108. The brush holder 102 includes a center hole 110 for accommodating the armature shaft 106 and commutator 108 once the motor is completely assembled. The brushes are disposed around the center hole 110 and are spring-biased so that the brushes normally extend into the center hole 110, as is known in the art.
Because the brushes are spring-biased to extend into the center hole 110, positioning the brush holder 102 over the armature shaft 106 requires pushing the brushes against their spring bias with a brush retainer (not shown) to prevent the brushes from obstructing the center hole 110 and then releasing when the commutator 108 is seated in the center hole 110 so that the brushes can contact the commutator 108 firmly.
Current motor structures often position an armature spring (not shown) on the armature shaft 106, which would pass through the center hole 110 during assembly. At times, however, the spring on the armature shaft 106 will contact the brush retainer and moves the retainer as the shaft 106 passes through the center hole 110, releasing the brushes prematurely before the commutator 108 is seated properly within the center hole 110.
There is a need for a device that retains brushes during assembly without experiencing the premature brush release problems of known devices.
Accordingly, the present invention is a combination brush retainer/spring assembly that includes a retaining ring connected to a spring to form a unitary device. The retaining ring is positioned in a center hole of a brush retainer and holds a plurality of brushes against their spring bias to prevent the brushes from obstructing an armature shaft as it passes through the center hole. Once the commutator is properly seated the center hole, the retaining ring is pushed away by the commutator to release the brushes.
After assembly, the conical spring is disposed on the armature shaft between the retaining ring and a ball bearing that is slip-fitted over the armature shaft. Once the motor is completely assembled, the conical spring is compressed so that a narrow end of the spring engages with an inner race of the ball bearing. The spring force in the conical spring forces the armature shaft and the ball bearing to rotate together at the same angular velocity without any slippage.
By connecting the retaining ring and the conical spring into a single brush retainer/spring assembly, the present invention prevents the brushes from releasing prematurely and blocking the center hole. Further, integrating the conical spring with the retaining ring into a unitary assembly allows the same assembly to retain the brushes and engage with the inner race of the ball bearing, thereby making brush retention more reliable and streamlining the manufacturing process.